This invention relates generally to a pneumatic radial tire for a passenger car, and more specifically to a pneumatic radial tire for a passenger car having an improved belt layer structure in order to improve high speed performance and driving confortableness of the tire and to reduce the tire weight.
Requirements for tires have become severer and severer in recent years with the development in highways, and steel radial tires have replaced conventional bias tires as the tires that satisfy these requirements.
In steel radial tires, a carcass layer having its reinforcing cords arranged substantially at 90.degree. to a tire circumferential direction is disposed between a pair of right and left bead portions and is covered with a plurality of belt layers reinforced by steel cords. Therefore, the steel radial tires exhibit various excellent properties as the tire in high speed performance, driving stability, wear resistance, low rolling resistance, and so forth.
However, the steel radial tire is not yet free from the problem that driving comfortableness is not high because a plurality of belt layers reinforced by the steel cords are hard and stiff.
In conjunction with the tire weight, the weight of the steel radial tire has been reduced recently to such a level which is substantially equal to that of bias tires of an equivalent size, but further reduction of the tire weight seems to have reached the limit.
Since a plurality of belt layers reinforced by the steel cords have great mass, the belt layers are likely to swell up due to the centrifugal force of the tire at the time of high speed rotation, whereby so-called "separation" is likely to occur at both end portions of the belt layers. Thus, the steel radial tire has reached the limit in the aspect of high speed performance, too.